Polyimide resins are produced using, as raw materials, a diamine and an acid dianhydride. In general, aromatic compounds are used for both of the diamine and the acid dianhydride as raw materials, and the resulting aromatic polyimide resins are in wide use as a film, a coating, an adhesive, a composite material, a separation film, etc. for their high heat resistance. Many of these aromatic polyimide resins, however, are low in solubility in solvents; therefore, when they are used, for example, as a coating, it is impossible to coat them as they are and it is necessary to coat a solution of a polyamic acid (a precursor) and then heat the coated solution to give rise to imidization; thus, aromatic polyimide resins have had poor processability.
Hence, various researches were made for improvement of polyimide resin. For example, in Japanese Patent Application Kokai (Laid-Open) No. 301958/1993 is disclosed a polyimide resin using, as raw materials, a tetracarboxylic acid dianhydride of a cross-linked hydrocarbon and a diamine having a cyclohexane ring; in Japanese Patent Application Kokai (Laid-Open) No. 157560/1995 is disclosed a polyimide resin block copolycondensate using an aromatic diamine as a raw material; in Japanese Patent Publication No. 5891/1996 is disclosed a polyimide resin using, as raw materials, a tetracarboxylic acid dianhydride of a cross-linked hydrocarbon and an aromatic diamine; and in Japanese Patent Application Kokai (Laid-Open) No. 208835/1996 is disclosed a polyimide resin block copolycondensate using, as a diamine raw material, tetrahydrodicyclopentadienylenediamine, hexahydro-4,7-methanoindanylenedimethylenediamine or the like.
These polyimide resins provided heretofore have excellent solubility, but have insufficient transparency and are unable to satisfy both of solubility and transparency.
The objects of the present invention lie in providing, by using a diamine of a particular cross-linked hydrocarbon as a raw material for polyimide resin, a polyimide resin which is soluble in solvents and high in transparency, a process for production of the resin, and a polyimide resin solution composition.
The present inventors made an intensive study in order to solvent the above problems. As a result, the present inventors found out that the above objects could be achieved by using, as the diamine, a 2,5(or 6)-bis(aminomethyl)bicyclo [2.2.1]heptane. The finding has led to the completion of the present invention.
The present inventors also found out that by using, as the diamine, two or more kinds of diamines containing, as an essential component, a 2,5(or 6)-bis(aminomethyl)bicyclo [2.2.1]heptane, not only the above objects could be achieved but also the resulting soluble copolycondensate polyimide resin had high adhesivity. The finding has led to the completion of the present invention.